The present invention relates to a swing actuator converting a forward and backward motion of a piston into a rotating and swinging motion of an output shaft coaxially positioned with the piston so as to output, and more particularly to a three-position stop type swing actuator which can stop the output shaft at a middle position of the rotation and swing.
In this kind of swing actuator rotating and swinging the output shaft, there is a case that it is required to stop the output shaft at the middle position of the rotation and swing.
On the contrary, the swing actuator which can stop the output shaft at the middle position of the rotation and swing can be realized, as shown in FIGS. 7 and 8, for example, by providing with a cylinder for a middle stop 3 having a large propelling force for stopping a rack at a moving middle position in a body of a rack and pinion type swing actuator 1.
The rack and pinion type swing actuator 1 is not particularly illustrated since a structure of itself has been already well-known, however, is structured such that a rack moving in forward and backward directions due to a fluid pressure and a pinion engaging with the rack are provided in an inner portion of the body 2, and an output shaft 4 rotating and swinging by the pinion is provided in a direction perpendicular to a moving direction of the rack.
On the contrary, the middle stop cylinder 3 has a piston having a larger propelling force than the rack, and the rack moved along a full stroke because the rack is not restricted by the piston when the piston is retracted, whereby the output shaft swings all around an angular range. Further, when the piston moves forward, the rack is brought into contact with the piston so as to restrict the stroke, so that the swing angle of the output shaft is limited.
In FIGS. 7 and 8, reference symbols 6a and 6b denote supply and discharge ports for supplying and discharging a compressed air to both ends in an axial direction of the rack, reference symbols 7a and 7b denote supply and discharge ports for supplying and discharging the compressed air to both ends of the piston of the middle stop cylinder 3, and reference numeral denotes a position detecting sensor for detecting moving positions of the rack and the piston.
As mentioned above, the swing actuator which can stop the output shaft at the middle position of the rotation and swing can be realized by providing with the middle stop cylinder in the rack and pinion type swing actuator, however, since the rack and pinion type actuator is structured such that an axis of the output shaft and an axis of the rack vertically cross to each other, a size in a direction perpendicular to the axis of the output shaft is increased.
An object of the present invention is to obtain a three-position stop type swing actuator having a small size in a direction perpendicular to an axis of an output shaft and a comparatively simple structure.
In order to achieve the object mentioned above, in accordance with the present invention, there is provided a three-position stop type swing actuator comprising: a main piston arranged within a casing in such a manner as to freely move in forward and backward directions due to a fluid pressure; an output shaft placed at a coaxial position with the main piston in such a manner as to be fixed in an axial direction and freely rotate around an axis; a conversion and transmission mechanism converting a forward and backward motion of the main piston into a rotating and swinging motion of the output shaft so as to transmit to the output shaft; and a sub piston arranged within the casing in such a manner as to freely move in the forward and backward directions due to the fluid pressure and be capable of being brought into contact with the main piston.
Further, in accordance with the present invention, there is provided a three-position stop type swing actuator comprising: a first cylinder hole provided within a casing in such a manner as to be communicated with each other, and having a small diameter and a large length in an axial direction; a second cylinder hole having a large diameter and a short length in an axial direction; a main piston arranged within the first cylinder hole in such a manner as to freely move in forward and backward directions in an axial direction; a sub piston having a large diameter portion sliding in an airtight manner within the second cylinder hole and a small diameter portion sliding in an airtight manner within the first cylinder hole, and restricting a middle stop position of the main piston by the small diameter portion being brought into contact with the main piston; a first pressure chamber formed in one end surface side of the main piston; a second pressure chamber formed between another end surface of the main piston and a small diameter portion of the sub piston; a third pressure chamber formed in a side of a large diameter portion of the sub piston; an output shaft placed at a coaxial position with the main piston in the casing in such a manner as to be fixed in an axial direction and freely rotate around an axis; and a conversion and transmission mechanism converting a forward and backward motion of the main piston into a rotating and swinging motion of the output shaft so as to transmit to the output shaft.
In the swing actuator having the structure mentioned above, when driving the main piston in a state of forward moving the sub piston, the main piston is brought into contact with the sub piston so as to stop at the middle position, so that the output shaft also rotates and swings in a limited manner at a corresponding angle. When backward moving the sub piston, the main piston moves together and reaches a predetermined stroke end, and the output shaft rotates and swings to a predetermined angular range in correspondence thereto.
As mentioned above, in accordance with the present invention, it is possible to convert the forward and backward motion of the main piston into the rotating and swinging motion of the output shaft arranged at the coaxial position with the main piston so as to output, so that it is possible to make the size in the direction perpendicular to the axis of the output shaft small in comparison with the rack and pinion type actuator.
In accordance with one embodiment of the present invention, the swing actuator has an adjuster for changing the middle stop position of the main piston by adjusting the stroke of the sub piston. The adjuster is constituted by a bolt, has an outer end portion for an adjusting operation protruding outward from the casing and an inner end portion fitted to an inner portion of the sub piston in such a manner as to freely slide relatively and is provided with an engaging portion engaging with the sub piston in the inner end portion.
In accordance with a particular embodiment of the present invention, the conversion and transmission mechanism includes at least one of first converting means converting a forward and backward motion of the main piston into a rotating and swinging motion of the main piston and second converting means converting the forward and backward motion of the main piston into the rotating and swinging motion of the output shaft.
The first converting means is constituted by a spiral groove formed on an outer periphery of the main piston and a pin fitted to the casing so as to best fitted to the spiral groove, and the second converting means is constituted by a spiral groove formed on an outer periphery of the output shaft and a pin fixed to the main piston so as to be fitted to the spiral groove.
The second converting means may be constituted by a screw having a lead angle larger than 45 degrees and formed on the outer periphery of the output shaft, and a nut formed in the main piston and meshed with the screw, in place of the spiral groove and the pin.